In numerous dental and orthodontic procedures, casts are made of the teeth of both the upper and lower jaws of a patient. These dental casts are then mounted on an articulator to reproduce the location and movement of the lower teeth and mandible relative to the upper jaw and maxillary teeth. Various methods of reproducing the teeth for the upper and lower jaws of patients and mounting them in gnathological articulators have been commonly employed in the prior art for a number of purposes, including the making of artificial dentures, gnathological positioners, etc. The importance of using instruments such as articulators is to approximate as closely as possible the patient's opening and closing axis of rotation or arc of closure of the jaws.
It is sufficient in terms of the present invention to understand that the position of patient's teeth in the upper and lower jaws and the relative positioning of the upper and lower jaws must be precisely reproduced in an articulator in order to permit the dentist or orthodontist to determine and carry out the corrective measures which are required for a given patient.
Face bows are commonly used in the prior art for transferring maxillary relationship data from patients to such articulators. See, e.g., U.S. Pat. No. 3,218,716 to Stuart. Present arbitrary face bows are used for recording and relating the patient's jaws and dentition to a universal reference plane and point (ideally the axis-orbital plane) oriented relative to the patient's head. These references serve an essential function in properly orienting and transferring spatial information to the dental casts on the articulator.
The face bow is the mechanical means by which data is transferred from the patient to the articulator and the dental casts mounted thereupon. The spatial orientation of the patient's dentition and jaws as well as the spatial orientation of the dental casts mounted on the articulator are correlated with each other by the references described above through the use of the face bow. The primary purpose for the face bow and the techniques involving the use of the face bow is to locate, transfer and reproduce as accurately as possible the patient's exact jaw location and movements on the articulator. Only in this way can the patient's dynamic occlusion be reproduced and studied. Prior art face bows have performed this function by establishing approximately the orientation of the patient's dental casts relative to a universal reference plane and axis. The face bow is then mechanically fitted onto the articulator to enable a dental cast of the maxillary teeth to be precisely mounted in the articulator. Subsequent transfer of additional dental casts from the patient to the articulator is also enabled using this technique without redetermining the articulator settings for each transfer.
Certain prior art face bows are of the "kinematic" type, and were designed to locate an opening and closing axis for the lower jaw or mandible. This axis can be described as the center of rotation about which the mandible moves at least during the first third of its opening movement (without translation) when the condyles are seated in the fossae.
In an effort to streamline upon the above-noted kinematic technique, "estimated" or "arbitrary" techniques evolved where the exact hinge axis or "true axis" for the mandible was estimated from various facial landmarks. The external auditory meatus (or ear hole) has become one of the most popular facial landmarks for locating the face bow. Accordingly, face bows which are located upon the patient's head by means of the auditory meatus are also commonly referred to as "ear bows" as well as "arbitrary", "estimated" or "anatomical" face bows.
A typical application for such an arbitrary face bow involves the initial preparation of accurate upper and lower dental casts of the patient's teeth. An interocclusal record of the patient's bite relationship is also taken, most commonly in softened wax. There are many different interocclusal bite relationships possible for a given patient. The most traditional and reproducible relationship is the specific jaw relationship commonly referred to as "centric relation". The wax record provides the information necessary to correctly orient the lower cast of the patient relative to the upper cast. The upper cast in turn is related by the arbitrary face bow to the universal reference plane on the patient's head. The arbitrary face bow mechanically records this relationship by using convenient features or facial landmarks of the patient. Currently, in addition to the external auditory meatus or ear hole as noted above, most arbitrary face bows employ the depression at the nasion or bridge of the nose in order to establish the necessary reference plane.
The position of the arbitrary face bow on the patient's head may be described by means of various reference planes which are well known in the prior art. Physical or mechanical conversion factors are commonly provided on the face bow so that the position of the arbitrary face bow on the patient's head approximates these reference planes.
One exemplary reference plane that was used was defined to exist between the tragus of the ear and the corner of the eye. Since this reference plane depended upon strictly facial landmarks, it could not be correlated with the skeletal structure of the patient, the reproducible mounting of the articulator, nor with a lateral cephalometric head film of the patient.
Accordingly, palpation reference landmarks were established to more closely approximate skeletal structures of the patient. An example of such a reference plane involved palpation or location by touch of the condyle and the lower rim of the bony orbit. However, it was found that palpation of the condyle is only a rough approximation of the patient's true axis.
The most sophisticated and reproducible reference plane is the "axis-orbital" reference plane. This reference plane involves location of the exact true axis so that it can be precisely correlated to articulators. In addition to the exact true axis, this reference plane is also located with respect to the lower rim of the orbit, by means of palpation or touch. This reference plane has not been correlated in the prior art to either cephalometric landmarks nor to facial landmarks in relation to the arbitrary face bow. However, the arbitrary face bow has been designed on the assumption that the face bow most nearly approximates the axis orbital plane. As described below, it has been found that this assumption is not correct and, that, as a result, prior art face bows fail to provide precise correlation between these various reference planes and an articulator.
Radiographs or head x-rays in the form of orthodontic cephalometric head films are also commonly used in an attempt to accurately correlate various reference planes to diagnostic instruments. This is because of their ability to clearly illustrate the relationship between various anatomical features of the patient. A variety of orthodontic reference planes in the form of cephalometric analyses are established from such head films, one of the most popular being the Frankfort Horizontal reference plane. This plane is located by means of the "Porion" (the external auditory meatus of the ear) and the "Orbitale" (the lower rim of the orbit). However, it has been found that this reference plane also often fails to correlate with various facial landmarks and with the articulator.
In other cephalometric analyses, various anatomical features of the patient are analyzed by means of angular and linear relationships established between the various anatomical features and reference planes of the patient. Again it has been found that there still remains a need for correlation of the lateral cephalometric head film analysis to the other various diagnostic instrumentation.
In general, in order to more accurately reproduce, diagnose and create a treatment plan for a given patient, it is necessary for the orthodontist to more precisely correlate one or more of these reference planes with various diagnostic instruments such as the articulator, referred to above, and to lateral cephalometric head films. Such a precise correlation, however, is not readily possible with existing techniques.
In any event, it is believed clearly apparent that dentists and orthodontists practice different variations of these techniques in diagnosing and treating patients. In practically all such existing techniques, the dentist and orthodontist now rely substantially on experience. Accordingly, there has been found to remain a need for a method and apparatus permitting more accurate transfer of data relating the patient to the lateral cephalometric head films or the like and to gnathological instruments such as the articulator. Accordingly, the present invention provides a means for more accurately reproducing spatial information and for correlating this information directly from the patient's reference planes, the patient's lateral cephalometric head film and to an articulator.